Title: Personalized Cancer Therapy Guided by Photoacoustic Chemical Imaging (PACI) of Tumor Microenvironment (TME) Abstract: Tumors are often found in an altered metabolic state, which leads to anomalous chemical composition, such as hypoxia (low oxygen level), acidosis (low pH level), and hyperkalemia (high potassium concentration). These three form a ?therapy resistance triad (O2, pH, and K+)?, suppressing cancer?s responses to radio-, chemo-, and immuno-therapy. As each triad member?s concentration is strongly relevant to cancer progress and response to therapy, a non-invasive, sensitive, and reliable approach for evaluating their temporal and spatial distributions in the tumor microenvironment (TME) in vivo, non-invasively, is highly desirable. To fill this serious and long-standing gap in technology, we introduce a novel set of O2, pH, and K+ sensing nanoprobes that, in combination with the emerging photoacoustic imaging technology, enables quantitative mapping of the O2, pH, and K+ levels in solid tumors in vivo. The central hypothesis of this proposed research is that, enabled by our photoacoustic chemical imaging (PACI) powered with sensitive chemical indicator nanoprobes, we can image and quantitatively evaluate the spatio-temporal distributions of the TME?s therapy resistance triad (O2, pH, and K+), at depths of up to a few centimeters, in vivo and in a non-invasive fashion, and then correlate with cancer responses to treatments via radio-, chemo-, and immuno-therapy. This hypothesis will be examined rigorously using orthotopic patient derived xenograft (PDX) breast cancer mouse models. To enable a comprehensive understanding of the technology?s capabilities, as well as limitations, the imaging results from PACI of the TME will be compared for a wide variety of PDX tumor models and treatment situations. To examine the central hypothesis, our research will focus on three specific aims: Aim 1. Understand tumor response to radio-therapy by PACI of the TME; Aim 2. Understand tumor response to chemo-therapy by PACI of the TME; and Aim 3. Understand tumor response to immuno-therapy by PACI of the TME. Potential impact: As the orthotopic PDX tumors faithfully resemble the original tumors in cancer patients, including their TME, chemical imaging of these PDX tumors, combined with studying the correlations of the imaging findings with the cancer responses to therapies, could have a large impact on translational research and clinical management of breast cancer, e.g. helping to discriminate the most suitable treatment plan or alternative plan for individual cancer patients. By the end of this funding period, we will objectively test and thoroughly verify whether the novel PACI technology powered by sensitive nanoprobes can image the TME?s chemical properties of PDX mouse tumors in vivo, non-invasively, for predicting the cancer responses to radio- , chemo-, and immuno-therapy. Once successfully validated, the proposed strategy could shed new light on imaging-guided personalized cancer medicine, so as to hopefully ensure an optimal treatment outcome.